1. Field of the Invention
This invention relates to a method and an apparatus for constructing an underground structure by propelling underground a plurality of preformed cylindrical bodies or by constructing an underground structure of a required shape in an underground area in the rear of preformed cylindrical bodies after they have been moved forward underground in a self-running manner.
2. Description of the Prior Art
The conventional methods and the apparatuses for advancing more than three cylindrical bodies underground have included many advancing jack arrangements of various types in the advancing facilities thereof. The number of locations at which such advancing jack arrangements must be provided increases according as the number of the cylindrical bodies to be moved forward increases. Hence, the mechanical facilities and the advancing operation of the conventional method and the apparatus are complex, extremely uneconomical and inefficient. Further, where a starting base is too short to have more than three cylindrical bodies constructed there, the advancing operation must be carried out with a necessary reaction force obtained from somewhere else. However, the conventional thrusting method in which the cylindrical bodies are to be propelled by thrusting jacks through struts with a reaction wall installed in the rear requires many huge struts. The thrusting method is thus inefficient and not only uneconomical but also tends to be hazardous because of jumping up or bending of the struts that likely takes place during the work there. The conventional pulling method requires many horizontal holes where it is impossible to obtain a necessary reaction force from the rear and is therefore also uneconomical.
Meanwhile, the conventional tunnelling method includes a shield driving method, Messel driving method, etc. However, in accordance with the conventional tunnelling method, boring and excavation work and assembling work on segments and timbering are to be performed in close vicinity to an excavation work area and thus cannot be performed independently of each other. Therefore, the boring and excavation work and the segment and timbering assembling work have to be alternately carried on. This requires a lengthy period of time for construction work. Besides, it is necessary to increase the strength of the segments and the timbering to make them strong enough against any horizontal axial force that is likely to be applied thereto. The conventional tunnelling method, therefore, is uneconomical because such an arrangement is required. In addition to that, this method often must be carried out at the risk of collapse of the excavated ground during the assembling work on the timbering.